1. Field of the Invention
The present invention relates to a power steering apparatus.
2. Description of the Related Art
Conventionally, as a power steering apparatus, there is a structure made to have a control valve for switching and connecting a pump side supply flow passage. It also has a tank side return flow passage to a first chamber and a second chamber of a power cylinder in accordance with a steering operation and interpose a damper valve between each of the first chamber and the second chamber of the power cylinder and the control valve. Further, the damper valve is structured, as described in Japanese Utility Model Application Laid-Open Publication No. 64-35180, to have a housing, a partition member for partitioning an inner portion of the housing into a power cylinder side and a control valve side, a first valve apparatus provided in the partition member and allows only a supply direction flow from the control valve side to the power cylinder side. A second valve apparatus provided in the partition member and applying a damping force to a return direction flow from the power cylinder side to the control valve side.
In this power steering apparatus, when steering to the right or the left, a fluid pressurized and fed by a pump is fed from the control valve to any one oil chamber of the first chamber and the second chamber in the power cylinder, and a propelling force is applied to a rack shaft passing through the power cylinder, thereby assisting the right or left steering force. At the same time, the fluid in another oil chamber in the power cylinder is returned to a tank via the control valve. Accordingly, when the steering force is neutral, the fluid pressurized and fed by the pump is returned to the tank from the control valve, whereby the fluid is not supplied and discharged to the first chamber and the second chamber of the power cylinder.
Further, in the power steering apparatus, the respective damper valves are connected to the first chamber and the second chamber of the power cylinder. Therefore neutral stability of the power cylinder at a neutral time of the steering operation is improved and a high-speed straight drive performance of the vehicle is improved. That is, at the neutral steering time, since the fluid is not supplied from the control valve side to the power cylinder side, the first valve apparatuses of the respective damper cylinders are in a closed state. The dosed state of the second valve apparatus is maintained as far as a road reaction force applied to the power cylinder is not over the damping force of the second valve apparatuses in the respective damper valves, whereby the fluid discharge from the first chamber or the second chamber of the power cylinder is not generated, and the power cylinder maintains an immobility, that is, the neutral stability is improved.
Thus, in accordance with the power steering apparatus provided with the damper valve, at a neutral steering time, with both damper valves respectively connected to the first chamber and the second chamber of the power cylinder, a valve plate constituting the second valve apparatus is attached (closely adhered) to the partition member, so as to close a through flow passage provided in the partition member. Accordingly, when supplying the fluid to the first chamber of the power cylinder, for example when turning to the left so as to discharge the fluid in the second chamber when steering input of a driver for starting the steering operation from the neutral state, the first valve apparatus of the damper valve connected to the first chamber is opened and the second valve apparatus of the damper valve connected to the second chamber is opened. However, the valve plate of the second valve apparatus applies a certain load (an attachment feeling) for removing the attachment between the valve plate and the partition member to the driver.
Further, for example, when turning to the left in which the fluid is supplied to the first chamber of the power cylinder, the valve plate constituting the second valve apparatus in the damper valve connected to the first chamber is attached (closely adhered) to the partition member so as to close the through flow passage provided in the partition member. Accordingly, when steering input of the driver for turning to the right from the leftward steering state, in order to discharge the fluid in the first chamber mentioned above, the now closed second valve apparatus of the damper valve connected to the first chamber is opened. At this time, the valve plate of the second valve apparatus applies a certain load (an attachment feeling) to remove the attachment between the valve plate and the partition member to the driver.
An object of the present invention is to remove a steering load felt by a driver when starting a steering operation from a neutral state and turning to the left or the right in a power steering apparatus provided with a damper valve.
According to the present invention, there is disclosed a power steering apparatus which has a control valve for switching and connecting a pump side supply flow passage and a tank side return flow passage to a first chamber. It also has a second chamber of a power cylinder in accordance with steering operation and interposing a damper valve between each of the first chamber and the second chamber of the power cylinder and the control valve, wherein a damper valve has a housing, a partition member for partitioning an inner portion of the housing into a power cylinder side and a control valve side, a first valve apparatus provided in the partition member and allowing only a supply direction flow from the control valve side to the power cylinder side, and a second valve apparatus provided in the partition member. Applying a damping force to a return direction flow from the power cylinder side to the control valve side, and wherein the damper valve has a cap attached to the housing and holds the partition member between the cap and the housing.